Add support for Python 3.4, pypy3, use travis_retry

http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/

Author: stefankoegl

.travis.yml

@@ -4,10 +4,12 @@ python:
   - "2.7"
   - "3.2"
   - "3.3"
+  - "3.4"
   - "pypy"
+  - "pypy3"
 
 install:
-  - pip install coveralls --use-mirrors
+  - travis_retry pip install coveralls
 
 script:
   - coverage run --source=jsonpointer tests.py